Device for distance measurement

ABSTRACT

A device for measuring distance with a visible measuring beam (11) generated by a semiconductor laser (10), a collimator object lens (12) to collimate the measuring beam towards the optical axis (13) of the collimator object lens (12), a radiation arrangement to modulate the measuring radiation, a reception object lens (15) to receive and image the measuring beam reflected from a distant object (16) on a receiver, a switchable beam deflection device (28) to generate an internal reference path between the semiconductor laser (10) and the receiver and an electronic evaluation device (25) to find and display the distance measured from the object. According to the invention, the receiver contains a light guide (17&#39;) with a downstream opto-electronic transducer (24), in which the light guide inlet surface (17) is arranged in the imaging plane of the reception object lens (15) for long distances from the object and can be controllably moved (18&#39;) from this position (18) transversely to the optical axis (14). In an alternative embodiment, the light inlet surface (17) is fixed and there are optical means (36) outside the optical axis (14) of the reception object lens (15) which, for short object distances, deflect the imaging position of the measuring beam to the optical axis (14) of the reception object lens (15). The measuring radiation is pulse modulated with excitation pulses with a pulse width of less than two nanoseconds.

BACKGROUND OF THE INVENTION

The invention relates to a device for distance measurement.

A device of this type is known from a publication from the company ofWild Heerbrugg AG, Switzerland, V.86, under the title "Distanzmessungnach dem Laufzeitmeβ-verfahren mit geodatische Genauigkeit" (Distancemeasurement according to the propagation time measurement method withgeodetic accuracy). It is also used for the measurement of distances toobjects having natural rough surfaces. Thus, in the surveying ofsurfaces which are difficult to access such as quarries, cavern walls,tunnel profiles, etc., in which distances up to several 100 m must bemeasured, devices are used in which pulsed infrared semiconductor laserdiodes with large emitting surfaces serve as radiation sources. Pulselengths of 12 nsec are used. The advantage of these radiation sourcesconsists in the fact that radiation pulses of high peak power in theorder of magnitude of several watts can be generated, with the resulttherefore that the required measuring distances of several 100 m can bereached. The accuracy is 5-10 mm. One disadvantage results from therelatively large dimensions of the emitting surface of these lasers ofthe order of magnitude of 300 μm. Such large dimension cause theradiation lobe from these devices to have a divergence of about 2 mrad,as a result of which, at only 50 m, a beam cross section of 0.1 m ispresent. In the case of a very short distance, the beam cross section ofthis device still has a diameter of several centimeters, since in orderto transmit the pulsed power of several watts at 2 mrad beam divergence,objective lens diameters of several centimeters are needed.

Since the transmitting and receiving objective lenses are arrangedseparately, for the near range below 10 to 15 m, an auxiliary lens mustbe fitted to cover the transmitting and receiving beams. A furtherdisadvantage consists in the fact that, because of the infraredmeasurement radiation, the point which is currently being measured onthe object is not detectable. In order to make the target visible, anadditional laser with visible radiation emission is provided, the beamaxis of which must be carefully adjusted to the transmitting beam axis.Such a device is equipped with an electronic evaluation and displaydevice, which also permits additional values to be entered via akeyboard and calculations to be carried out.

Likewise, a distance measuring device with separate transmitting andreceiving objective lenses is known from DE 40 02 356 C1. Thetransmitting device contains two electronically complementary-switchablelaser diodes, one of which sends the light wave trains on the measuringpath, the other sending the light wave trains on the reference path.Both light wave trains are alternately received by the samephotoreceiver, which is connected to an electronics evaluation means.Whether the laser diodes emit visible light cannot be gleaned from thepublication. The distance range to be measured is specified as 2 to 10 mand the measurement accuracy is intended to be in the range of a few mm.

In the journal "Industrie", November 1992, pages 6-8, a distancemeasuring device DME 2000 from the Sick GmbH company is described. Thedevice carries out an optical distance measurement on the basis ofpropagation time measurement, and operates with two semiconductor laserdiodes emitting visible light. The required transmitting light isgenerated by a laser diode with collimator optics, and the second laserdiode supplies the necessary reference signal directly to the receiver.The transmitting beam and the receiving beam are arranged to be coaxialto each other, so that only one single objective lens of relativelylarge diameter is used. The measuring distance to natural rough surfacesis 0.1 to 2 m with a light spot diameter of about 3 mm. For greaterdistances from the object, up to 130 m, a reflector film must be appliedto the object to be measured. The light spot diameter at these distancesis about 250 mm. In conjunction with the coaxial transmitting-receivingoptics, a relatively large-area PIN photodiode is used as receiver.Hence, although an overlap of the strongly divergent receiving lightcone with the transmitting beam is achieved, with the result thatdistances down to 0.1 m can be measured, no great measurement ranges canbe achieved with these large-area detectors without additionalreflectors.

In the construction industry, in particular in internal construction andin the installation industry, it is necessary to be able to measuredistances of up to 30 m on rough surfaces without the additionalreflectors. In the case of a required measurement accuracy of 1 to 2 mm,the divergence of the receiving beam must be as small as possible, sinceotherwise the ambient light proportion received at the same time wouldgenerate too large a noise signal in the receiver. A small divergence ofthe receiving beam of about 2 mrad, however, has the disadvantage that,in the case of separate transmitting and receiving optics, an overlap ofthe receiving beam with the transmitting beam is only present after 1 to2 m, so that only distance measurements beyond this distance arepossible.

SUMMARY OF THE INVENTION

The invention was therefore based on the object of making possible adistance measurement to natural rough surfaces in the entire distancerange from the front edge of the measurement device up to at least 30 musing a strongly collimated visible measuring beam which, in the nearrange, has a diameter of less than 0.5 cm and, in the distant limitingrange, a diameter of 1 to 2 cm. The accuracy of the measurement in thiscase is intended to lie in the millimeter range.

This object is achieved by a distance measuring device according to theinvention.

According to the invention, the collimator objective lens generates astrongly focused measuring beam along its optical axis. The optical axisof the receiving objective lens, arranged alongside, runs at leastvirtually parallel to the optical axis of the collimator objective lensand lies with the latter in a common plane. The unavoidable divergenceof the measuring beam, the relatively closely adjacent optical imagingsystems and the focal lengths of this system have the effect that ameasuring beam reflected at objects up to about 2 m proximity is imagedvirtually at the focal point of the receiving objective lens. As aresult of the concentration of the received light in a small area, nointensity problems arise for the signal evaluation even out as far asthe remote measured distances.

For small measured distances, however, it is to be observed that theimage position of the measured spot reflected at the object isincreasingly remote from the focal point longitudinally and transverselyto the optical axis of the receiving objective lens. The light guideentry surface, arranged at the focal point, then receives no more light,as a result of which the lower measuring limit is reached. According toone embodiment of the invention, the light guide entry surface tracksthe displacement of the image position of the measuring spot,specifically only transversely with respect to the optical axis of thereceiving objective lens. Tracking along the optical axis can bedispensed with, since intensity problems in respect of the measuringbeam reflected at near objects do not arise. It has even been provedthat tracking into the correct image position leads to overdriving ofthe evaluation electronics. The controllably displaceable light guideentry surface offers, for all measured distances, the capability ofadaptation to the optimal signal level.

A solution which is an alternative thereto consists in arranging thelight guide entry surface in a stationary manner and taking care, byoptical deflection means, that the measuring beams which, in the case ofshort distances from the object, are increasingly more obliquelyincident on the receiving objective lens, are deflected towards thelight guide entry surface. Here, too, use is made of the knowledge thata deflection which is correct in terms of imaging optics is not needed,since intensity problems do not arise in the case of close distancesfrom the object. This solution is advantaged in that it manages withoutmoving elements in the receiving channel.

An effect which limits the measuring accuracy of the device according tothe invention results from the physical properties of the modulatedlaser radiation in conjunction with the rough surfaces to be measured.

The visible radiation of the semiconductor laser diodes is emitted as aspectrum of equidistant spectral lines (modes). During the action of themodulation current, both the wavelengths and also the radiationdensities (intensities) of the modes change. Dependent on thewavelength, different modulation phase shifts of the laser pulsetherefore result in relation to the electric modulation pulse. In thiscase, the modulation phase relates to the time median t_(s) of theintensity variation I(t) over the emission duration t of the laser pulseduring one modulation pulse. Mathematically, t_(s) is equal to theintegral over I(t)*t*dt divided by the integral over I(t)*dt, theintegration range being equal to the entire laser pulse duration.

Based on the type of modulation and modulation pulse width, modulationphase differences that vary according to the wavelength can correspondto laser pulse time delays of up to 1.3 ns. The corresponding apparentdistance differences go up to 200 mm.

The light scattered back from the rough surface to be measured has agranular intensity distribution because of the coherence of the laserradiation, and this is known under the designation speckles. Only in thedirection in which the laser radiation would be reflected if the roughsurface were a mirror, do the speckles of the various modes of the laserradiation coincide. Because of the different wavelengths of the modes,this is not the case for all other directions, so that a radiation fieldis present with spatially different modulation phases.

The radiation which is incident on the receiving objective lens and isfed to the photodetector has a representative modulation phase which isproduced as the result of the averaging, weighted with the correspondingintensity, over all the modulation phases of the radiation fieldincident on the objective lens. This measured average of the modulationphases fluctuates according to the speckle structure over the radiationfield, that is to say according to the structure of the rough surface.By displacing an object which has a surface, which appears to bemacroscopically uniform, at right angles to the measuring direction, itcan be detected that the distance error corresponding to this modulationphase fluctuation can be up to 20 mm.

Surprisingly, it was proved that a decisive improvement in the physicalcondition can be achieved simply by the modulation of the laser diodesbeing generated using excitation pulses of which the pulse width issmaller than 2 ns. Depending on the wavelength, the modulation phasedifferences between all modes of the light reflected and falling on theobjective lens then become so small that the corresponding distancefluctuations become smaller than 2 mm.

The use of light guides in distance measuring devices is known per se.In conjunction with the present subject matter of the invention, theparticular advantage results in that the waveguide can be curved manytimes in its course towards the optoelectronic converter. By this means,the above-described weighted averaging over all the modulation phases isadditionally supported.

To compensate for drift effects in the electronics and in theoptoelectronic converters, it is known that, before and after theexternal distance measurement, by way of comparison, known lengths aremeasured via an internal reference path. For this purpose, in thesubject matter of the invention, a light-scattering element is switchedinto the collimated measuring beam in such a way that no radiationpasses via the external light path. The scattering characteristic ofthis element is matched to the spatial range over which the light guideentry surface is adjusted. As a result, two advantages which areessential for the functioning of the device are achieved. On the onehand, it is achieved that radiation from each part of the measuring beampasses into the light guide entry surface, as a result of whichdifferences in the modulation phase over the cross section of themeasuring beam have no influence on the distance measurement. Since theradiation is scattered by the light-scattering element in the entirespatial range in which the light guide entry surface is moved, thereference measurement can be carried out in any position of the lightguide entry surface, immediately and without renewed readjustment of theposition, as a result of which a short measuring time is achieved. Thescattering intensity per unit area can be adjusted such thatover-driving of the evaluation device is reliably avoided. This measuretherefore has significance not only for the arrangement with anadjustable light guide entry surface but also in the same way for thealternative arrangement having a stationary light guide entry surfaceand additional beam deflection means.

BRIEF DESCRIPTION OF THE DRAWINGS

The device according to the invention is described in more detailhereinafter using exemplary embodiments represented schematically in thedrawing, further advantages also being described. In detail:

FIG. 1 shows an overall representation of the device with an adjustablelight guide entry surface, in top view,

FIG. 2 shows a receiving part having a mirror for beam deflection,

FIG. 3 shows a receiving part with refractive beam deflection,

FIG. 4 shows a receiving part with diffractive beam deflection,

FIG. 5 shows a beam splitter used in the transmitting beam and

FIG. 6 shows a deflection prism which can be switched into thetransmitting beam.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1, a semiconductor laser 10 generates a variable measuring beam11 which is emitted through a collimator objective lens 12 in thedirection of the optical axis 13 as a parallel beam and has a diameterof about 4 mm. The optical axis 14 of the receiving objective lens 15runs at least approximately parallel to the optical axis 13 of thecollimator objective lens 12 and lies with the latter in one plane. Thediameter of the receiving objective lens 15 is about 30 mm and theacceptance angle about 120°, so that, on the one hand, the beam crosssection for radiation intensities reflected from far-removed objects 16is sufficiently large, and on the other hand, the radiation reflectedfrom near objects at a large angle of incidence can be accepted.

Far-removed objects 16 appear to lie at infinity for the receivingoptics 15, so that the image location of the measured spot produced onthe object lies on the optical axis 14 at the focus of the receivingobjective lens 15. The light guide entry surface 17 is arranged here inits basic position. The end of the light guide is surrounded by a mount18 which is fastened to a leafspring 19. The other end of the leafspring19 is rigidly clamped to the housing 20 of the distance measuring deviceand therefore forms a spring joint. The leafspring 19 rests underpretension on an eccentric 21 which can be rotated by a motor about anaxis 22. The mount 18 is moved during the rotation of the eccentric 21,for example into the position 18', transversely to the optical axis 14.The adjustment travel is about 3 mm in a practical exemplary embodiment.In the position 18', radiation is received from a near object, which isindicated by the receiving beam drawn with a dashed line. The adjustmentof the light guide entry surface runs approximately in the focal planeof the receiving objective lens 15. The correct image position of thenear measuring spot lies, as can be seen, behind the focal plane in thelight direction.

Instead of the adjusting device, selected in the exemplary embodiment,having a spring joint and an eccentric, other constructionalconfigurations are possible, such as slides or multiple-joint elements.

The front section of the light guide 17' can move freely, so that it canfollow the adjustment of the mount 18. In its rear section 23, it isfixedly curved many times. At its end, an optoelectronic converter 24 isconnected downstream of the light guide exit surface. The receivedsignals are fed to an evaluation device 25.

Inserted in the region of the measuring beam 11 emerging from thehousing 20 of the device is a low-reflection silvered termination disk26 which, for the suppression of reflections, can also be set obliquelyto the beam. In order to avoid residual stray radiation getting to thelight guide entry surface 17, a tubular aperture stop 27 is alsoprovided. Arranged in front of the light entry opening of this aperturestop 27 is a switchable beam deflection device 28 which can be pivotedby means of a motor about an axis 29. The surface of the beam deflectiondevice 28 on which the measuring beam 11 falls is a scattering, surfacethat generates a divergent scattering cone 30 being. The opening of thescattering cone 30 in the region of the light guide entry surface 17 issufficiently large for radiation from the reference light path thusproduced to be received in all positions of the light guide entrysurface 17.

The evaluation unit 25 also contains the electronics for modulation ofthe semiconductor laser 10. To adjust the emission direction of thesemiconductor laser 10 to the optical axis 13 of the collimatorobjective lens 12, the housing of the semiconductor laser 10 can bemounted so as to pivot about an axis 31 or an axis at right anglesthereto. The adjustment can be motor-controlled via the evaluationdevice 25 as a function of a selected received signal. To compensate forslight faulty adjustments of the optical axes 13, 14 to a common plane,it can also be advantageous to be able to adjust the light guide entrysurface 17 not only in the plane of the optical axes 13, 14, but also atright angles thereto. By means of a suitable scanning movement in thefocal plane of the receiving objective lens 15, the location having anoptimum signal level can be determined and the signal evaluation can beundertaken in this position of the light guide entry surface 17.

The evaluation device 25 contains a display device 32 and a keyboard 33via which, for example, correction values or information supplementaryto the actual distance measurement can be entered. An importantsupplementary item of information is the taking into account of thehorizontal position or vertical position of the plane defined by the twooptical axes 13, 14, in order to be able to measure actually at rightangles to the object. For this purpose, the device can be assigned, forexample, a two-axis electronic inclinometer 34, the horizontal axes ofwhich lie in the plane of the optical axes 13, 14 and are alignedparallel and at right angles to these axes.

The output signals from the inclinometer 34 can be fed to the evaluationdevice 25 and automatically taken into account during the distancemeasurement. However, they can also be used for the mechanicaladjustment of the semiconductor laser 10 or an active optical element,not shown, in the transmitting beam path, in order to level thecollimated beam automatically.

Apart from an item of information about the inclination of the device inspace, taking into account the azimuth, that is to say the angle atwhich the measuring beam is incident on the measured object surface inthe horizontal plane, expands the capabilities of the distancemeasurement, to be specific in the form of a polar registration of themeasured values. For this purpose, the device can be assigned a digitalmagnetic compass 35, of which the azimuth reference direction is alignedparallel to the optical axis 13 of the collimator objective lens 12. Aplurality of distance measurements, taking into account the inclinationand the azimuth of the measuring beam, allow in a manner known per sethe determination of points and areas in space and also thedetermination of the position of areas in relation to each other from asingle measuring location. Likewise, the computational determination ofhorizontal distances is possible, as is otherwise only possible in thecase of measurement systems having mechanical axes, electronictachymeters.

The front surface, the rear surface or else the center of the housing 20of the device can be defined as the zero point of the measurement andcan optionally be entered, for example via the keyboard 33, into theevaluation device 25 and automatically taken into account by the latterduring the distance measurement.

FIG. 2 shows a first possible solution for deflecting the beam reflectedfrom near object surfaces in the direction of a stationary light guideentry surface 17. Used for this purpose is a planar mirror 36, which isarranged outside the optical axis 14 and oblique to it, but which canalso be lightly curved and scattering. The expedient shape, arrangementand configuration can easily be determined by means of trials. Tocompensate for any crooked positions present between the optical axes13, 14, it can be particularly expedient to design the mirror in a torusshape around the optical axis 14. The arrangement described has theadvantage that the radiation received from distant objects is notinfluenced by the deflection means.

In FIG. 3, as a further possibility for deflecting the obliquelyincident measuring beams, a prism 37 is provided as refractive element.Here, too, the most expedient arrangement of the prism 37 can bedetermined by trials in which, on the one hand, the radiation receivedfrom distant objects is not deflected to such an extent that intensityfluctuations occur and, on the other hand, a sufficient proportion ofthe obliquely incident measuring beams are deflected in the direction ofthe light guide entry surface 17. It can in particular be advantageousto arrange the refractive surface to be ring-symmetrical to the opticalaxis 14, and to leave a part in the center uninfluenced. The prism 37can also be switchable, so that it becomes effective only in the case ofsmall distances from the object.

FIG. 4 shows a further possibility for the direction-dependent beamdeflection with the aid of a diffractive element 38. Such elements aregaining increasing importance as a result of the development ofmicrostructuring technology for holographic elements, zone plates andbinary optics. A review of the configuration and application of suchelements can be found in a publication from the Centre Suissed'Electronique et de Microtechnique S.A., on Diffractive OpticalElements (DOE), June 1991. The advantage of these elements lies in thefact that the diffractive structure can be matched to individual imageproperties. In this case, even complicated optical transformationfunctions can be realized relatively simply. In particular, adiffraction structure can be calculated and producedphotolithographically to deflect beams that are incident from differentdirections in the same direction. The acceptance angle of the objectivelens 15 in the direction of the transmitted beam can thus besignificantly enlarged.

An expansion of the field of application of the device according to theinvention results from the use of a rotatable two-beam prism in theemergent collimated measuring beam. As shown in FIG. 5, for this purposethe terminating disk 26 can be removed and a tube 39 can be insertedinto the tubular aperture stop 27 in its place. A prism 40 with a beamsplitting cemented surface 41 is inserted into the tube 39. In thismanner, an additional visible beam can be generated at right angles tothe optical axis 13 of the measuring beam, through an opening 42 in thetube 39. This beam can be used, for example, to place on a surface whichis present in order to be able to measure distances at right angles tothis surface. In the case of a device directed at right angles to theobject to be measured, distance values to other surfaces can also betransmitted using the additional beam.

The auxiliary means, shown in FIG. 5, for generating an orientation beamat right angles to the measuring beam can also be modified in a mannerknown per se by means of prisms having a plurality of splitter surfacesor other beam deflection means, such as in the case of a pentaprism.

A further task of the auxiliary means can consist in deflecting theoptical axis 13 of the measuring beam in the direction of the opticalaxis 14 of the receiving objective lens 15. Such a configuration isshown in FIG. 6. It has the advantage that even objects resting on thefront side 20' of the housing 20 reflect radiation into the receivingbeam path. For structural reasons related to the mounting of theobjective lens 15, it is advantageous in this case to offset thereceiving objective lens 15 somewhat into the housing 20. The prism 43,provided for the deflection of the beams, is arranged on a slide 44which, during the measurement of very short distances, can be pushedinto the beam path by hand.

The outlay on functional elements for the device according to theinvention is low and the elements are suitable for miniaturization. Thedevice can therefore be configured to be very compact and in particularas a pocket device.

We claim:
 1. A device for distance measurement, comprising:a visiblemeasuring beam (11) generated by a semiconductor laser (10), acollimator objective lens (12) for collimating the measuring beam (11)along an optical axis (13) of the collimator objective lens (12), acircuit arrangement for modulating the measuring beam, a receivingobjective lens (15) for receiving and imaging the measuring beam (11)reflected at a distant object (16) onto a receiving device, a switchablebeam deflection device (28) for generating an internal reference pathbetween the semiconductor laser (10) and the receiving device, and anelectronic evaluation device (25) for determining and displaying adistance to the object (16), wherein the receiving device includes alight guide (17') with an optoelectronic converter (24) connecteddownstream thereof, an entry surface (17) of the light guide (17') beingarranged in an image plane of the receiving objective lens (15) forlarge distances to the object and being controllably displaceable fromthis position transversely to an optical axis (14) of the receivingobjective lens (15).
 2. A device for distance measurement, comprising:avisible measuring beam (11) generated by a semiconductor laser (10), acollimator objective lens (12) for collimating the measuring beam (11)along an optical axis (13) of the collimator objective lens (12), acircuit arrangement for modulating the measuring beam, a receivingobjective lens (15) for receiving and imaging the measuring beam (11)reflected at a distant object (16) onto a receiving device, a switchablebeam deflection device (28) for generating an internal reference pathbetween the semiconductor laser (10) and the receiving device, and anelectronic evaluation device (25) for determining and displaying adistance to the object (16), wherein the receiving device includes alight guide (17') with an optoelectronic converter (24) connecteddownstream thereof, an entry surface (17) of the light guide (17') beingarranged along an optical axis (14) of the receiving objective lens (15)in an image plane of the receiving objective lens (15) for largedistances to the object, and optical means (36; 37; 38) being providedbetween the receiving objective lens (15) and the light guide entrysurface (17), outside the optical axis (14) of the receiving objectivelens (15) for short distances to the object, such that the imageposition of the measuring beam (11) is deflected by the optical meanstowards the optical axis (14) of the receiving objective lens (15). 3.The device according to claim 1, wherein the measuring beam is pulsemodulated with excitation pulses each having a pulse width below twonanoseconds.
 4. The device according to claim 1, wherein the light guide(17') has a plurality of curves along its length.
 5. The deviceaccording to claim 1, further comprising a mechanical adjusting device(18, 19, 21, 22) for adjusting a position of the light guide entrysurface (17) in a plane which is defined by the optical axes (13, 14) ofthe collimator objective lens (12) and receiving objective lens (15). 6.The device according to claim 5, wherein the adjusting device canadditionally be adjusted at right angles to the plane defined by theoptical axes (13, 14).
 7. The device according to claim 5, furthercomprising a motorized drive with a control device for moving theadjusting device over a predetermined adjustment range (18'), such thata light intensity received at the light guide entry surface is optimumfor signal evaluation.
 8. The device according to claim 7, wherein theadjusting device comprises a spring joint (19) with a motor-driveneccentric (21, 22).
 9. The device according to claim 1, wherein theswitchable beam deflection device includes a light-scattering element(28) having a scattering characteristic (30) that is matched to theadjustment range (18, 18') of the light guide entry surface (17). 10.The device according to claim 2, wherein the optical means includes areflector (36) inclined with respect to the optical axis (14) of thereceiving objective lens (15).
 11. The device according to claim 2,wherein the optical means includes a refractive optical element (37)arranged along an edge region of the receiving objective lens (15). 12.The device according to claim 2, wherein the optical means includes adiffractive optical element (38) arranged adjacent to the receivingobjective lens (15).
 13. The device according to claim 2, furthercomprising an electronic inclinometer (34) for measuring an inclinationof the optical axis (13) of the collimator objective lens (12).
 14. Thedevice according to claim 13, wherein output signals of the inclinometer(34) are fed to the evaluation device (25) as additional input signals.15. The device according to claim 13, wherein output signals of theinclinometer (34) are fed to an actuator for leveling the collimatedmeasuring beam (11).
 16. The device according to claim 2, furthercomprising a two-axis electronic inclinometer (34) for measuring aninclination of the optical axis (13) of the collimator objective (12)and an inclination of the plane formed by the optical axes (13, 14) ofthe collimator objective lens (12) and of the receiving objective lens(15).
 17. The device according to claim 2, further comprising a digitalmagnetic compass (35) for aligning an azimuth reference directionparallel to the optical axis (13) of the collimator objective lens (12).18. The device according to claim 2, further comprising a prism (40, 41;43) arranged between the collimator objective lens and the distantobject.
 19. A device for distance measurement, comprising:a visiblemeasuring beam (11) generated by a semiconductor laser (10), acollimator objective lens (12) for collimating the measuring beam (11)along an optical axis (13) of the collimator objective lens (12), acircuit arrangement for modulating the measuring beam, a receivingobjective lens (15) for receiving and imaging the measuring beam (11)reflected at a distant object (16) onto a receiving device, a switchablebeam deflection device (28) for generating an internal reference pathbetween the semiconductor laser (10) and the receiving device, anelectronic evaluation device (25) for determining and displaying thedistance measured to the object (16), and an electronic inclinometer(34) for measuring an inclination of the optical axis (13) of thecollimator objective lens (12), wherein the measuring beam is pulsemodulated with excitation pulses each having a pulse width below twonanoseconds, and wherein output signals of the inclinometer (34) are fedto an actuator for leveling the collimated measuring beam (11).
 20. Thedevice according to claim 19, wherein the receiving device includes alight guide (17') having an optoelectronic converter (24) connecteddownstream thereof, the light guide (17') having a plurality of curvesalong its length.
 21. The device according to claim 19, wherein theelectronic inclinometer comprises a two-axis electronic inclinometer(34) for measuring the inclination of the optical axis (13) of thecollimator objective lens (12) and an inclination of the plane formed bythe optical axes (13, 14) of the collimator objective lens (12) and ofthe receiving objective lens (15).
 22. The device according to claim 19,further comprising a digital magnetic compass (35) for aligning anazimuth reference direction parallel to the optical axis (13) of thecollimator objective lens (12).
 23. The device according to claim 19,wherein output signals of the inclinometer (34) are fed to theevaluation device (25) as additional input signals.
 24. The deviceaccording to claim 19, further comprising a prism (40, 41; 43) arrangedbetween the collimator objective lens and the distant object.
 25. Adevice for distance measurement, comprising:a semiconductor laser forgenerating a laser beam; a collimator objective lens for collimating thelaser beam along an optical axis of the collimator objective lens andguiding the laser beam toward a distant object; a receiving objectivelens for receiving and imaging the laser beam reflected from the distantobject along an optical axis of the receiving objective lens, theoptical axis of the receiving objective lens being parallel to theoptical axis of the collimator objective lens; a light guide having anentry surface at which the laser beam imaged by the receiving objectivelens is received, a position of the entry surface being adjustable in adirection transverse to the optical axis of the receiving objectivelens; a switchable beam deflection device for generating an internalreference path between the semiconductor laser and the entry surface; anoptoelectronic converter connected to the light guide for converting thelaser beam received at the entry surface of the light guide toelectrical signals; and an electronic evaluation device for determiningthe distance measured to the distant object based on the convertedelectrical signals.
 26. The device according to claim 25, furthercomprising a circuit for pulse modulating the laser beam to have pulsewidths below two nanoseconds.
 27. The device according to claim 25,wherein the light guide has a plurality of curves along its length. 28.The device according to claim 25, further comprising an electronicinclinometer for measuring an inclination of the optical axis of thecollimator objective lens.
 29. The device according to claim 25, furthercomprising a two-axis electronic inclinometer for measuring aninclination of the optical axis of the collimator objective and aninclination of a plane formed by the optical axes of the collimatorobjective lens and of the receiving objective lens.
 30. The deviceaccording to claim 29, further comprising a digital magnetic compass foraligning an azimuth reference direction to be parallel to the opticalaxis of the collimator objective lens.
 31. The device according to claim29, wherein output signals of the inclinometer are fed to the evaluationdevice as additional input signals.
 32. The device according to claim28, further comprising an actuator for leveling the collimated laserbeam, the actuator being controlled in accordance with output signalsfrom the inclinometer.
 33. The device according to claim 25, furthercomprising a motorized drive for moving the position of the entrysurface over a predetermined adjustment range such that a lightintensity received at the entry surface is optimum for signalevaluation.
 34. The device according to claim 33, further comprising aspring biasing the entry surface to a neutral position.
 35. The deviceaccording to claim 34, wherein the motorized drive includes an eccentricmember for moving the entry surface away from the neutral position.